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The Mad Fermentationist

Monday, October 1, 2012

There's no shortage of bourbon-barrel-aged Russian Imperial Stouts or Barleywines at most beer bars; they seem to be about the only styles that most brewers think to age in the ubiquitous charred-American-oak vessels. I enjoy some of them, especially the smooth chocolaty stouts, but I’d prefer to see more breweries thinking of new ideas rather than jumping on something that has already been done so well (e.g., Founders Kentucky Breakfast Stout, Pelican Mother of All Storms, Firestone-Walker Parabola, Great Divide Barrel Aged Old Ruffian etc.).

Thanks to my 70 qrt mash tun, the 25 lb grain bill wasn’t much of a challenge. Luckily I checked the gravity of the wort as it was coming to a boil and noticed it was slightly lower than I calculated it needed to be to hit the massive original gravity (~1.108). I had stopped the run off when I reached my pre-boil volume, so I collected and then boiled the final runnings on the stove until the main wort was ready for the first hop addition. The concentrated wort didn’t get thick enough to caramelize (like first runnings of my Scottish Stout) but it contained enough sugar to boost the OG of the batch by .009. The ability to make adjustments like this on the fly is one of the reasons it is a good idea to check the gravity of the wort as early as possible.

The biggest issue on this batch for me was generating enough yeast without the ability to repitch from a yeast cake. I started a single vial of WLP833 (German Bock Lager) in a 1.5 L starter on my stir-plate. After two days, I crash cooled it, let the yeast settle, decanted the spent wort, and started it back with 1.7 L of fresh starter wort. While this second starter wasn’t much larger, pitching more than twice as many cells into it allowed for a bit more growth than occurred in the first stage. In this case (according to the Mr. Malty Pitching Rate Calculator) pitching a month old vial of yeast into a 1.5 L stir-pate starter resulted in 230 billion cells. Pitching those cells into a 1.7 L starter got me all the way up to 540 billion cells. Not quite the “ideal” 830 billion cells the calculator calls for in 5.75 gallon of 1.108 lager, but not that far off. Despite under-pitching, the chilled starter was enough to produce a good krausen within 12 hours in the 46 F wort.

I had initially planned to lager this beer pre-barrel-aging, making it the second beer into the malt whisky barrel, but lagering after it soaks up some booze should provide time for it to mellow. Yesterday I brewed a 1.080 rye stout that will go into the barrel as soon as the Weizen-Trippelbock has enough character... I'm not against the classics!

9/22/12 Decanted and made a new 1.7 L starter to get the yeast rocking for tomorrow's brew. Quick aggressive fermentation.

Brewed 9/23/12 by myself

Weyermann Heritage Floor Malted Wheat was used, even though I doubt it will add much in such a flavorful recipe.

Collected 8.25 gallons of 1.082 runnings with a batch sparge. Collected an extra gallon of final (1.055) runnings to boil down as I was a bit under-gravity. Added the now 1.100 reduced runnings back at the same time as the first hop addition.

Chilled to 85 F with ground water, then used recirculated ice water to get it down to 47 F. 90 seconds of Pure O2, and pitched the un-decanted starter which had been sitting in the fridge at the intended fermentation temperature. Left at 46 F to ferment.

9/26/12 60 hours after pitching, raised temperature to 49 F to ensure continued strong attenuation. Raised 1 F each day after that until it reached 54 F.

10/2/12 Moved out of the fridge to 62 F for a diacetyl rest and strong finish to fermentation. Gravity only down to 1.043, but still some activity evident.

10/8/12 Racked to the five gallon Balcones whisky barrel, first use after swirling around a few ounces of Knob Creek. Gravity down to 1.029 (73% AA, 10.6% ABV), still some yeast in suspension. It would have been nice to give it another week to settle, but it will have a few weeks at cellar temp for the yeast to finish out anything they were working on. Left at 66 F to age.

10/28/12 Racked to a keg, dropped the temperature to 35 F for a couple months of lagering. Big boozy character, hot, but not rough.

1/16/13 Down to 1.025 (small drop from the liquor in the barrel, or final attenuation while warm). Warmed to 64 F a few days before bottling. Made a starter of WLP833 24 hours in advance, left on the stir plate for 12 hours, then turned it off to ensure no oxygen would be left. Added 2.75 oz of table sugar to the 5 gallon yield. Aiming for about 2 volumes of CO2. Left at 64 F to carbonate, hopefully.

2/18/14 Tasting notes, with a comparison to the original batch. Carbonation was slightly lower than I intended. Not sure if the yeast stalled, or if that is 2.0. Otherwise pleased with it, probably would go 5.0-5.5% Extra Dark Crystal next time and leave the Dark out to boost the dried fruit character.

Gravity points are pretty easy to deal with mathematically. One gallon of 1.055 runnings will add 55 points. So dividing them by the volume of the batch gives you their gravity contribution, 55/5.8=9.5. You just need to extend the boil to ensure you get down to your target volume as well. This method only really works for strong beers, lower alcohol beers won't have final runnings that are nearly as dense.

I have a fridge with a digital temperature controller. The increase doesn't have to be that precise, but you always want the temperature to be rising towards the end of fermentation.

Actaully, I think you may have underpitched more than you think. You are spot on for those cell counts with the first 1.5 liter starter but you won't get much yeast growth in the second starter the way you did it.

The ideal conditions for growing yeast in stepped starters is a 1:10 dilution in cells. Without diluting that first starter, there will be not enough substrate (sugars) in the culture to grow more yeast. You basically maintained the culture and fermeneted it. You need to have the subtrate in vast excess to get great growth, hence the 1:10 dilution.

So what I normally do is when my second starter is ready to go, I'll 1/10th of my first starter and use that to inoculate. I'll then cold crash the first while the second starter is going. When the second starter is done, then I'll decant and add back to the first. You can then use this for a third starter, etc...

When I do this I can sometimes get 800 billion cells in 3 liters (depends on strain of coruse)/

Good to know. Are you saying the the initial cell count has nothing to do with the total number of cells (given the same volume, gravity, and method)? The second step was in 1.060 wort, rather than my usual 1.040, so hopefully that gave them more substrate to grow on.

Happily the gravity of the beer has been dropping to about where I expected it to. As of Tuesday it was down to 1.040. Still a small krausen, hoping it gets down to 1.025-1.030. Should be ready to go into the barrel by Wednesday when I head to Denver.

In a sense. Yeast growth kinetics is not linear, but exponential. That means the fastest rate growth occurs earlier when the yeast do snese limiting substrate.

So if you start with 100 billion cells and pitch 1 liter of stirred starter wort (1.040), it is very hard to double the amount of cells you have (linear). When I do this I get about 180 billion cells max. However, when I take 1/10th of this starter (18 million cells) and make another 1 liter starter I get close to 150 billion cells (exponential). This would be the equivalent of taking a smack pack and adding it to 3-4 liter starter (I have to check mr malty on this).

So the initial cell count is important, but just as long as there is not too many cells.